Method of collecting trace samples for analysis

ABSTRACT

A hand held sampling method is carried out using apparatus have a handle, a head connected to the handle and a mechanism for retaining a substrate on the head. The substrate is preferably a sheet-form flexible substrate which is mounted so as to present a collection portion thereof for collection of a sample. The substrate is preferably of a dimension so as to be readily fitted into the inlet portion of an analyzer. The apparatus is manipulated so that the collection portion of the substrate traverses surfaces of interest. The substrate is then removed and placed at the inlet of an analyzer for desorption of a sample. The apparatus enables an area to be sampled quickly and efficiently, while keeping a user&#39;s hands away from the surface, and this enables otherwise inaccessible areas to be sampled. It does not require any intermediate transfer steps, transferring a sample from a collection media to another substrate for subsequent analysis.

This application is a Divisional application of application Ser. No.08/627,196 filed Apr. 3, 1996 and now U.S. Pat. No. 5,859,375.

FIELD OF THE INVENTION

This invention relates to the collection from surfaces of samples oftrace particles or liquids, or other compounds for chemical detection byvarious analytical means, such as an ion mobility spectrometer (IMS),gas chromatography (GC), liquid chromatography (LC), mass spectrometry(MS) and other methods, the compounds being present either as traceswithin particles or as discrete particles or aerosols, droplets or thelike. The invention more particularly relates to the detection ofexplosives, narcotics, and other contraband concealed by individuals intheir belongings or in transported goods and cargo, or in vehicles andaircraft. However, the invention also encompasses environmental samplingsuch as chemical warfare agent liquid droplets and aerosols which areextremely toxic and for which no hand contact can be tolerated.

BACKGROUND OF THE INVENTION

The removal of dust as a simple household task from domestic dwellingshas been and is still carried out with dust cloths. In moresophisticated situations, chatelaines and housekeepers have employedmaids, butlers and valets equipped with white gloves or mittens toremove dust, polish silverware and furniture. Previously, there has beenno necessity or interest in analyzing the collected dust particles.Rather, the sole intent was to collect and throw out dust and dirtparticles.

The necessity to collect dust and particles for analysis is a morerecent requirement. With the advent of terrorism where explosives can beconcealed to create undetectable bombs and also with drug smugglersconcealing their drug shipments, the need for trace/forensic detectionhas become necessary. While early explosives detectors relied on thecollection of atmospheric explosives vapours, modern high powerexplosives are plastic with extremely low vapour pressures therebypresenting vapour detection instruments with extremely difficultdetection situations to the point of impossibility. Modern plasticexplosives can have vapour pressures 5 or 6 orders of magnitude lowerthan the traditional volatile explosives such as nitroglycerine (NG),trinitrotoluene (TNT) and ethylene glycol denitrate (EGDN). For example,U.S. Pat. No. 4,909,090 teaches the use of hand operated vapour samplerswhich heats the surface to assist in dislodging vapours which aretrapped on collector surfaces in the probe. However, with the very lowvapour pressure of plastic explosives and drugs this method is extremelylimited in its usefulness. Drugs like cocaine, heroine and others alsohave very low vapour pressures and thus are undetectable by existingvapour detection instruments.

Modern detection equipment can detect extremely low levels ofexplosives, narcotics and the like, in the range of nanograms orpicograms. However, this simply raises the problem of obtaining asuitable sample. Accordingly, rather than attempt to collect a vapoursample, an alternative approach of particle collection and analysis wasproposed, notably by Barringer, et al, and followed by others, both forforensics purposes as well as for surface geochemical exploration wheretrace metals and organometals can be useful as pathfinder indicators inmineral exploration activities. Earlier patents have covered theseapplications, such as Barringer U.S. Pat. Nos. 3,970,428; 4,220,414;4,192,176; and 5,425,263.

Particle collection techniques include: surface inspection by means ofphysical particle collection in minute amounts; the use of dustpan-brush arrangements; vacuum suction onto porous or semi-poroussubstrates, filters, membranes and the like; the use of swabs, swipes,gloves, etc. One such method is described in U.S. Pat. No. 5,476,794which describes the removal of particles with a glove and the use of anintermediate step, that of vacuum suction off the glove. Thesetechniques have been the subject of earlier patents, which havedeveloped into more sophisticated techniques incorporated into variousinstrumental devices for direct analysis, including plasma opticalemission spectrometers, optical analyzers and mass spectrometers amongothers.

Gloves, mitts and swipes have been used in various forms for particlecollection. Disadvantages exist with these earlier systems ofcollection. The major disadvantage of most of these earlier techniquesis that an intermediate step is required to transfer from such a gloveor the like any particles/trace chemicals so collected for presentationto the analytical device. One method is to use a suction device tovacuum the glove or mitt, as in U.S. Pat. Nos. 5,476,794. Not only doesthis present a loss of time and cause nuisance to the operator, but thesecondary stage is inefficient, causing a loss of sample due toincomplete transfer from the glove. Additionally, vacuum suction devicesare noisy, cumbersome, and require power to energize the suction motors.Even small vacuum hand samplers have relatively limited battery life. Ifa positive hit is obtained, then usually the suction device iscontaminated and has to be cleaned thoroughly before being used again.Finally, often an even greater problem is created by the suction causingglove/cloth fibers and lint to be released which can either obstruct thecollecting substrate, present interfering chemicals or fluff/lint whichmight compete in the analytical process, as for example, if IMS is usedwhere matrix effects from the hand covering material may well competetoo aggressively in the ionization process.

Sampling materials or cloth which cover the fingers are also known forcollecting particles from surfaces. These have the advantage of avoidingthe intermediate step and use of a suction device. Such sampling clothsor finger covers unfortunately leave the fingers vulnerable to damagefrom sharp objects or exposed corners, hot objects or surfacescontaminated with toxic chemicals. Finger swabs/hand mitts can alsobecome dislodged during search operations when pressed into tight areas.

Finally the problem of cross-contamination remains, in that if ahand/finger is in direct contact with the swab, or glove/mitt, there isalways the possibility that the hand/fingers will become contaminatedwith the analyte sought and pass this over as false positive alarms orhits onto subsequent samples. Also in some sampling situations, such asChemical Warfare (CW) agents/liquid droplets, the chemical toxicity ofthe sample is too dangerous to allow close contact with hands.

As described in U.S. Pat. No. 5,476,794, particles are transferred fromthe glove to a collection probe, and the complete probe is inserted intothe analyzer to vaporize the samples. The major disadvantage with thistechnique is the complexity of the sampling probe, the ease with whichit can be clogged by debris and lint off gloves, and its complexity andhence cost.

An alternative means to collect trace particles is to use small filterdiscs which are inserted into the suction line of a vacuum cleaner unitto efficiently remove by suction the particles required for analysis.The substrate discs are positioned immediately at the sampling head toprevent particles lodging in the suction line and becoming dislodged ata later time thereby giving false anomalies. The collection substratemust be porous enough to allow air suction while at the same time besufficiently dense to entrap the particles in the size range ofinterest. After a collection time adequate to collect a sufficientquantity of dust/material for analysis, the filter disc or substrate isremoved and presented for analysis, as for example to an ion mobilityspectrometer (IMS). The filter disc is inserted into a thermaldesorption device which is rapidly heated to volatilize the collectedmaterial. The heating process converts the trace particles to vapoursfor conventional chemical vapour analysis, such as might be made by anIMS, mass spectrometer or gas chromatography or such other instrument.

The disadvantage of this technique is that it is still possible that thevacuum cleaner can become contaminated. More importantly, it requiresmanipulating a cumbersome vacuum cleaner to obtain a sample. Bearing inmind that only trace samples may be available, it is highly desirable tobe able to quickly and efficiently gather particles from the surfaces ofluggage, vehicles etc.

SUMMARY OF THE INVENTION

In accordance with earlier application Ser. No. 08/627,196, there isprovided a hand held sampling apparatus for collecting a sample of atleast one of solid particles, aerosols, droplets and trace chemicals ona substrate which is in sheet form and comprises a central workingportion and an edge portion substantially extending around the centralworking portion, for analysis in an analyzer, the apparatus comprising:a handle; a head connected to and extending from the handle andincluding a bore and a retaining means for retaining the substratewithin the bore, for presenting the working portion for collection ofthe sample and for enabling mounting and removal of the substrate fromthe apparatus, the head also including a projection means movable,relative to the retaining means, between an open configuration, spacedfrom the retaining means to permit insertion and removal of thesubstrate, and a closed configuration, in which the retaining meanssimultaneously traps the edge portion of the substrate between theretaining means and the projection means, with the projection meansprojecting through the bore whereby the working portion projectsoutwardly.

Advantageously, the head is connected to the handle by a shaft, whichshaft spaces the head from the handle. Preferably, the projection meanscomprises a boss adapted to project through and beyond the bore.

To facilitate mounting and removal of the substrate, the boss isadvantageously mounted on an arm or plate, which is pivotally mountedwith respect to the handle.

The apparatus can include a light means within the projecting body forilluminating an area being sampled and/or a suction means connected tothe holes for drawing air through the projecting body, to enhancecollection of particles on a substrate.

The invention of that earlier application can be provided in combinationwith a substrate for collection of particles. The substrate is sheetform and comprises a central collection or working portion and an edgeportion. More preferably, the substrate is chemically inert, is devoidof any dyes and colouring materials, and is such as to be capable of amechanical wiping action, without removing from the substrateappreciable amounts of lint and fibers, and the substrate is capable ofelevated temperatures for thermal desorption and pyrolysis processes.The substrate can be woven and can comprise one of cotton, Teflon, andfibreglass. The substrate can be chemically treated to enhance itsability to collect and entrap at least one of desired particles,droplets and chemical agents, and the substrate material can bechemically treated to modify the chemistry thereof during desorption,and pyrolysis cycles.

The invention provides a method of collecting a sample of at least oneof particles, aerosols, droplets and trace chemicals, the methodcomprising the steps of:

(1) providing a substrate having a central working portion and an edgeportion substantially extending around the working portion and mountingthe substrate in a hand held sampling apparatus comprising a handle, ahead connected to the handle and means retaining the substrate, by theedge portion of the substrate, on the head, so that the working portionof the substrate is presented for use;

(2) manipulating the apparatus so that the collection portion of thesubstrate traverses surfaces of interest;

(3) removing the substrate from the apparatus and inserting thesubstrate into the inlet port of an analyzer;

(4) operating analyzer to desorb any sample collected and analyzing thesample.

In step (3) the substrate is removed by grasping an edge portionthereof, without contacting the working portion.

It is expected that the present invention will provide a consistentdegree of performance and reliability in the collection ofdust/particles, aerosols or droplets required for analysis. While theinvention is expected to have particular applicability to collection ofparticles of explosives and drugs, it is not restricted to this and maybe of use on other compounds which may be aerosol or liquid, as forexample, which can be experienced CW agent detection, the verificationof decontamination, etc.

Since the substrate does not continuously contact the hands/fingers andneed not contact them at all, possible allergies effects are prevented.It is known that latex gloves and fibreglass can cause allergies to thehands of the searchers.

Finally, the use of the substrate holder allows several such samples tobe in use in conjunction with one analyzer. If hand swabs/gloves/mittsare used, general operational practice is that one should await theresult of the swab analysis before proceeding to the next sample toavoid the possibility of contamination, a situation which does not occurwith the present apparatus since each sample is unique and presented assuch for analysis. It is known that if multiple objects are beingsampled any trace particles picked up on one object/surface can betransferred off the glove/mitt to the second or subsequentobject/surfaces, which can cause considerable difficulties in thesearching procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show moreclearly how it may be carried into effect, reference can now be made, byway of example, to the accompanying drawings, in which:

FIG. 1a is a perspective view of a first embodiment of a collectiondevice in accordance with the present invention;

FIG. 1b is a side view of the first embodiment;

FIG. 2a is a perspective view of a second embodiment of a collectiondevice in accordance with the present invention;

FIG. 2b is a side view of the second embodiment;

FIG. 3 is a perspective view of a third embodiment of a collectiondevice in accordance to the present invention;

FIGS. 4a and 4b are side views showing engagement of a retaining ring;and

FIG. 5 is a schematic view showing an inlet of an IMS analyzer andinsertion of a substrate for analysis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, a first embodiment of the apparatus forcarrying out the present invention is generally denoted by the reference10. The apparatus 10 has a handle 12. Extending from the handle 12 is ashaft 14, and at the end of the shaft 14, a head 16. The handle isshaped to provide easy and comfortable operation, while spacing theuser's hand from the operating head 16, as detailed below, so as toprotect the hand from injury and contamination.

The shaft 14 includes a slot 18 through which extends a substrateretaining arm 20. A pin 22 connects the retaining arm 20 to the shaft 14and provides a pivotal connection.

A first, outer end 24 of the arm 20 includes a resilient protrusion orboss 26, which comprises a base portion 26a and a resilient, spongelayer 26b. A disposable pad 28 is mounted on the sponge layer 26b, byany suitable means. The pad 28 and layer 26b together are resilientenough to enable a substrate to closely follow a surface underinspection.

A second end 30 of the arm 20 is adapted to engage a retaining clip 32.The clip 32 can comprise any suitable clip arrangement, including asimple spring clip or some hinged catch or lever. The arm 20 is shown inan open configuration, with the protrusion 26 raised to permit insertionand removal of a substrate. In the closed configuration (not shown), thesecond end 30 is retained by the clip 32. The clip 32 provides easy andrapid locking and unlocking of the arm 24, to permit positioning andremoval of a sample substrate. Any suitable form of clip can be used,and this may comprise a spring-type latch or an element that requiresmanual actuation.

The head 16 includes a main circular part having a ring 34 of generallyuniform cross-section. This ring 34 has a generally planar top surface36, and a rounded conical bottom surface 38. It defines a central bore40 which is cylindrical.

A substrate is indicated at 45 and the substrate is chosen to providegood efficiency for particle collection and retention. As such, thesubstrate 45 is chemically inert, mechanically robust, and does not shedcotton, lint of fluff. It should be formed from a material that is ableto withstand high temperatures in any subsequent desorption process, orthermal cleaning process. Preferably, the substrate is a woven sheetmaterial, formed from a single fiber, which has not been subsequentlytreated by dyes or any other substances, so as to be chemically inert.Substrate 45 could be formed from Teflon (Polytetrafluoroethylene)fibers or cotton, for example.

Where it is desired to use the apparatus 10 close to electricalapparatus and the like, an insulator 42 can be provided between thehandle 12 and head 16.

In use, the retaining clip 32 is unlatched, if necessary, to raise thearm end 24 to an open position. A substrate 45 is then located over thebore 40. The apparatus is then closed, by bringing the arm end 24 downuntil the retaining clip 32 is engaged. This causes the boss 26 and pad28 to extend into and through the bore 40. Consequently, substrate 45 isshaped to a rounded, domed profile as shown. The substrate 45 then hasan exposed working portion 46, outside of and below the bore 40, and anedge or retaining portion 47 trapped between the boss 26 and the head16. The edge portion 47 extends out through the bore 40 and issufficiently large to adequately secure and retain the substrate 45. Theedge portion 47 should also be large enough to enable the substrate 45to be readily handled, without contacting the working portion 46.Indeed, to facilitate this, it is possible that the edge portion 47could be marked or otherwise identified. This could be achieved bycolouring the edge portion 47, subject to the requirement that thesubstrate must be inert.

The substrate 45 could be provided with a coating indicated at 48, toenhance its ability to collect and entrap at least one of desiredparticles, droplets and chemical agents. The substrate coating caninclude a chemical treatment to modify the chemistry of the substrateduring desorption and pyrolysis cycles. Further, the coating 48 caninclude means for trapping particles electrostatically.

With the substrate 45 secured in position, the handle 12 can be used torun the working portion 46 of the substrate over surfaces of interest.For example, the working portion 46 can be readily run over the exteriorof suitcases, the various surfaces of cars or other vehicles, etc. Theapparatus 10 can enable the substrate 45 to access places not readilyaccessible by hand, for example, areas within the engine compartment ofa vehicle, or around suspension and chassis components of a vehicle. Italso enables areas around, for example, electrical components or otherhazardous locations to be accessed for inspection. It is also possiblethat the handle 12 can be adapted to be fitted to some extension pole orthe like, to further increase the effective range. This would enablevarious surfaces towards the top of transport trucks or transportationcontainers, to be readily examined.

Once the required area or surface has been sampled, the retaining clip32 is released, and the arm end 24 raised to release the substrate 45.The edge portion 47 of the substrate is then grasped, taking care not tocontact the working portion 46. Then, as shown in FIG. 5, the substrate45 is inserted into the desorption stage of an IMS analyzer 50. It willbe appreciated that the IMS analyzer 50 is shown purely by way ofexample, and that the invention is applicable to a wide variety ofanalyzers, as noted above. IMS analyzers are well known in the art, andare described in U.S. Pat. Nos. such as 5,405,781 and 5,071,771. Thesubstrate 45 is inserted into a platen 51, located above an anvil 52,and this includes means to align the collection or working portion withthe analyzer inlet. The anvil 52 is moveable vertically, and is drivenby an electromechanical drive 54. The anvil 52 is raised, to press thesubstrate 45 against an entry port 56 of the IMS analyzer 50. A heater58, within the anvil 52 is then activated, to vaporize and desorb asample, indicated at 60 on the substrate 45. The vaporized sample isthen entrained in a flow of air or other gas through the anvil 52,indicated at 62 and passes through the entry port 56 into the IMSanalyzer 50 for analysis.

The dimensions of the working portion 46 and edge portion 47 and thesubstrate 45 are such as to correspond with the dimensions of theanalyzer 50. Thus, the edge portion 46 abuts a seal 64 around the entryport 56, and the working portion 46 coincides with the heater 58 fordesorption.

After desorption, the substrate 45 should effectively be clean. Ifnecessary, all of it can be subject to a subsequent, high temperaturecleaning step, to ensure that any remaining contaminants or portions ofa previous sample are driven off. The substrate 45 can then be returnedto a supply of clean substrates, ready for use.

The shape of the protrusion 26 and pad 28 correspond to the bore 40, toensure that the substrate 45 is securely retained in position duringsampling and to cause the substrate to adopt the desired profile. Thisprevents the head 16 from becoming contaminated during sampling. Hence,once a substrate 45 bearing a possible sample is removed, the apparatus10 merely needs to be fitted with a new or clean substrate 45, to beready for use again. The retaining clip 32 can provide a quick releasefriction grip.

FIG. 2 shows an alternative embodiment. For simplicity and brevity, likecomponents are given the same reference as in FIG. 1, and theirdescription is not repeated.

Here, the retaining arm 20 is replaced by a hinged or pivoted plate 70,with the head, here indicated at 16a being provided with a straight edgealong which is located a hinge 72. The protrusion or boss 26 anddisposable pad 28 are then provided on the plate 70. The plate 70includes, along its free edge, a clip element 74 that engages a clasp orsecondary clip element 76, carried on the portion of the head 16a,joining the head to the handle 12.

Here, the clasp 76 is of a half moon type, which is rotated to engagethe clip element 74.

In use, this second embodiment 70 would be used in much the same manneras the first embodiment 10. Again, if desired, an insulator can beprovided between the head 16a and handle 12, to permit usage on theelectrical equipment and the like.

Turning to FIGS. 3 and 4, these show a third embodiment, generallyindicated by the reference 80. This third embodiment 80 has a handle 82connected by an insulator 83 to a head 84.

The head 84 is connected by a quick disconnect fastener 86. This is toenable the head 84 to be removed as an integral part of the substrate,i.e. so that the substrate and head would be treated as a singleelement. Alternatively, if the substrate is routinely removed from thehead, it enables the head 84 to be removed for cleaning and the like.

The head 84 comprises a generally cylindrical body 88 having one freeend and another end connected by the insulator 83 to the handle 82. Thiscan be provided with a layer of resilient sponge material or the like,as the layer 28 or the first embodiment, and can have a rounded end.

A substrate is indicated at 90, and is mounted around the head 84. It ispreferred to use a generally planar, sheet form substrate 90, which isdimensioned to fit within the inlet of the appropriate analyzer, as forthe other embodiments. The substrate 90 will likely need to be folded atthe edges, to fully conform to the head 84. The substrate 90, as for thefirst embodiment, includes a working portion 91 and an edge portion 92.

The edge portion 92 is retained by a retaining ring 94, or any othersuitable retaining means adjacent the other end of the head 84. Theretaining ring 94 slides over the substrate 90 and traps the edge of thesubstrate against the base of the body 88. Securing lugs 96 are mountedon the head 84, and the lugs 96 engage and retain the ring 94 in anysuitable manner. Here, the lugs 96 are shown as being pivotally mountedwith a collar 97 having a conical cam surface, for locking the lugs 96in an engaged position. The ring 94 could alternatively engage the lugs96 by a screw or bayonet action, or be provided with magnetic attractionto the head 84, so as to secure the substrate 90 in position.

The head 84 can be formed so as to provide illumination through thesubstrate 90. For this purpose, the head 84 will need to be, at least tosome extent, transparent or translucent. Similarly, the substrate 90will need to permit transmission of light. Then, a light 98 can bemounted in the head 84. The handle 82 stores batteries, to power thelight 98, and an appropriate operating switch can be provided.Additionally, or alternatively, battery power stored in the handle 82can be used to drive a small suction motor to draw air into and throughthe head 84, to assist in collecting particles on the substrate 90.Suction holes, indicated at 100 could then be provided on the head 84.The handle 82 can include a handle cap 102, for replacement ofbatteries, in known manner.

In use, this embodiment is used in a similar manner to the otherembodiments. A substrate 90 is mounted on the head 84 and run oversurfaces of interest. Again, an extension of handle (not shown) can beprovided. After collection of a sample, either the substrate 90 isremoved from the head 84, or the whole head 84 is removed, by way of thequick disconnect fastener 86. Where it is possible that the head 84 mayhave become contaminated, then it will be desirable to replace the head84 with another head that has been cleaned. In any event, to insert thesubstrate 90 into an analyzer, it will be removed from the head 84together with the ring 94, again by just grasping the edge portion 92,to prevent contamination of an operator's hands. The ring 94 will thenbe carefully removed and the substrate 90 is then inserted into theanalyzer inlet.

While preferred embodiments have been described, it will be appreciatedthat numerous variations and modifications are possible within the scopeof the present invention. Various arrangements can be conceived tofollow the sampling concept of non-contact between the substrate and thesearcher's hands so as to avoid contamination, an aspect of the greatestconcern to organizations such as police, army and customs servicesengaged in search operations. Recognizing that current, sensitiveanalytical instruments can detect as low as 1 pg levels of drugs andexplosives, it will be appreciated just how critical it becomes to keepthe searcher's hands free from close contact with the substrate. Thesearcher will be instructed to carefully remove the substrates forpresentation to the analyzer, by carefully handling the substrate at itsedge. It is also to be appreciated that the substrate can be composed ofelectrically conducting mesh, of a size appropriate to the particlerange to the collected. Then the conductive mesh substrate can be useddirectly in a desorbing/pyrolysis stage in which the particles are flashdesorbed by the rapid heating of the metal mesh by the passage ofelectric current through it. The substrate can also be such as toattract and hold particles, droplets etc., electrostatically. Thesubstrate can also be chemically treated to enhance its ability tocollect and entrap substances that the user wishes to collect, such asparticles, droplets and chemical agents. Thus, the substrate can bechemically treated to modify the chemistry thereof during desorbtion andpyrolysis cycles, to enhance collection of the desired substances.

The present invention has the advantage that the profile of thesubstrate is sufficiently raised, during sampling, to allow goodall-around contact with the surfaces/objects under inspection. Thesubstrate is pressed through the bore of the head aperture in thesampler to contact the surfaces or objects to be sampled. The handleallows extended reach to access more difficult areas, or areas whichmight be hot, dirty or be close to moving machinery or electricalsources. Telescopic extensions can be provided to the handle to obtainsamples from locations normally out of the reach of the person using aswab/glove or hand covering. There is ease in decontamination becausethe scrubber pad is easily removed and discarded. Since the pads aresmall and are of low cost to manufacture, there is no economicdisadvantage in using this discard protocol.

The collection substrate is presented to the analyzer by inserting thesubstrate into a slot of matching geometrical shape and size which isthen transposed to the desorption stage, so no intermediate sampletransfer step is required. At the desorption stage, and anvil is raised,heated and sealed against the inlet to an IMS analyzer. A key benefit ofcontrolling the geometry of the substrate surface which can be allowedto make contact with the surfaces under inspection is that it can bemade to match the analyzer inlet geometry perfectly. That is, theanalyte is centrally collected and correspondingly aligned and presentedto the analyzer. The IMS analyzer has sufficient sensitivity for thedetection of the desired analytes, and their identifications arepre-programmed into the IMS analyzer. Analyzers such as the IMS havebeen well described in the literature and have also been the subject ofnumerous patents. While the invention is described in terms of analysisusing IMS, it will be obvious to those experienced in the art that thesubstrates can be made into forms and shapes suitable for introductionto other types of analyzers, such as gas chromatographs orchemiluminescent detectors, mass spectrometer and the like.

We claim:
 1. A method of collecting a sample of at least one of particles, aerosols, droplets and trace chemicals, the method comprising the steps of:(1) providing a substrate having a central working portion and an edge portion substantially extending around the working portion and mounting the substrate in a hand held sampling apparatus comprising a handle, a head connected to the handle and means retaining the substrate, by the edge portion of the substrate, on the head, so that the working portion of the substrate is presented for use; (2) manipulating the apparatus so that the collection portion of the substrate traverses surfaces of interest; (3) removing the substrate from the apparatus by grasping an edge portion thereof without contacting the working portion, and inserting the substrate into the inlet port of an analyzer; (4) operating the analyzer to desorb any sample collected and analyzing the sample.
 2. A method as claimed in claim 1, when carried out with an analyzer which has a heatable anvil which can be raised against the inlet port, and which has provision for a gas flow, wherein steps (3) and (4) comprise:(a) placing the substrate between the anvil and the inlet port; (b) displacing the anvil towards the inlet port, to seal the substrate between the anvil and the inlet port; (c) heating the anvil to heat the substrate to desorb and vaporise any sample present; (d) providing a flow of gas through the anvil and the substrate into the inlet port, to entrain any vaporised sample; (e) operating the analyzer to detect substances of interest.
 3. A method as claimed in claim 1, or 2 which includes mounting the substrate by substantially all of the edge portion thereof and causing the central working portion to project outwardly from the edge portion, for contact with surfaces of interest.
 4. A method as claimed in 3, which includes: providing the head with a retaining means, a bore and a projection means; and the method comprising spacing the projection and retaining means apart in an open configuration to permit insertion of the substrate, and pressing the projection means and the retaining means together into a closed configuration, to trap the edge portion of the substrate between the projection and retaining means with projection means causing the working portion to project outwardly, the projection means and the retaining means being subsequently displaced to the open configuration for removal of the substrate.
 5. A method as claimed in claim 4, which includes providing the projection means with a boss and a resilient layer, providing resilient support to the substrate.
 6. A method as claimed in claim 4, which includes providing an arm pivotally mounted to the handle and mounting the projection means on one end of the arm, and providing a retaining clip means between the handle and the other end of the arm for retaining the arm in a closed configuration, in which the retaining and projection means engage and secure the substrate, the method including: pivoting the arm and the handle to the open configuration; inserting the substrate; pivoting the handle and the arm to the closed configuration to trap the edge portion of the substrate between the projection and retaining means, and securing the arm and the handle in the closed configuration with the retaining clip means; and, after traversing the substrate over surfaces of interest, releasing the retaining clip means, displacing the arm and the handle to the open configuration and removing the substrate for insertion into the inlet part of the analyser.
 7. A method as claimed in claim 3, which comprises providing the head with a projecting body and mounting the substrate around the projecting body, and providing the retaining means at the end of the projecting body remote from a free end thereof.
 8. A method as claimed in claim 7, which includes providing the retaining means in the form of a ring, and wherein after mounting of the substrate on the projecting body, the method includes sliding the ring over the substrate to retain the substrate in position, and after collection of a sample by traversing the substrate over surfaces of interest, displacing the ring off the substrate to permit removal of the substrate.
 9. A method as claimed in claim 7, which includes providing illumination from within the projecting body to illuminate a surface being sampled.
 10. A method as claimed in claim 7, which includes providing a plurality of holes in the projecting body and drawing air through the substrate and through those holes, to enhance collection of particles on the substrate.
 11. A method as claimed in claim 1, or 2 which includes providing a substrate which is chemically inert, is devoid of any dyes or coloring materials and is such as to be capable of a mechanical wiping action without removing from the substrate appreciable amounts of lints and fibers.
 12. A method as claimed in claim 11, which includes treating the substrate by one of: a chemical treatment to enhance its ability to collect and entrap at least one of desired particles, droplets and chemical agents; and a treatment to modify the chemistry of the substrate during desorption and pyrolysis cycles.
 13. A method as claimed in claim 11, which includes providing a substrate which is woven and comprises one of cotton, polytetrafluoroethylene and fiberglass. 